The invention relates to a system for connecting optical distribution lines and optical junction lines to an exchange, said lines respectively connecting subscribers to exchanges and interconnecting exchanger in a wideband multiservice telecommunications network such as the BISDN network or the switched remote distribution network, the system of the invention enabling lines to be tested automatically and enabling faulty junctors to be replaced by spare junctors
An optical line for distribution or for junction purposes and conveying signals relating to both directions of a call by means of two different optical wavelengths, is constituted:
either by two optical fibers each conveying signals in one of the directions of the call, each fiber being connected at one end directly to a transmission circuit including an optoelectronic component such as a laser, and being directly connected at its other end to a reception circuit containing an optoelectronic component such as a PIN diode, with said transmission and reception circuits situated at the same end of the line constituting the optoelectronic interface which may constitute:
a line junctor in the exchange;
terminal equipment on subscriber premises; or
a junction junctor in a remote exchange;
or else by a single optical fiber conveying signals in both directions of the call and connected at each of its ends to optical duplexing means having two other outlets is connected to a transmission circuit and the other one of which to the reception circuit of a junctor in an exchange or of terminal equipment on subscriber premises, or of a junction junctor.
The assembly constituted by a line and the interface circuits connected to the ends thereof constitutes a link.
If any of the components in a link is faulty, then that link is unavailable and service is interrupted for a period of time depending on the time required to detect the fault and the time required for repairing it.
Like other telecommunications networks, wideband multiservice networks make use of a very large number of links such as those described above. Although the unit failure rate of links is low, the large numbers thereof naturally give rise to a relatively large number of breakdowns that must not only be detected and analysed, but which must also be repaired in order to ensure good quality service.
The arrangements for detecting breakdowns in links and for remedying failures while minimizing immediate maintenance activity constitute "link securization".
The securization of subscriber telephone lines constituted by pairs of copper wires connected to respective junctors is a known problem: numerous circuits have been described that make use of electromechanical relays inserted on the lines and operating under the supervision of control circuits both to connect lines and junctors to test apparatus and also to connect lines to spare junctors.
In French patent number FR-A-2 503 500 (=U.S. Pat. No. 4,451,708), for "A subscriber terminal security circuit", the circuit described makes use in the exchange of at least one spare terminal or unit comprising a plurality of spare terminals connected to the trunk(s) interconnecting subscribers lines and test equipment via an isolating circuit, and capable of replacing any of the terminals corresponding to the subscriber lines connected to the test trunks by switching over the test trunk connection relay of any given faulty terminal or by switching over the test trunk connection relays of the terminals in the unit including a faulty terminal.
In French patent number FR-A-2 555 388 (=U.S. Pat. No. 4,594,704), "A subscriber terminal security circuit in a digital concentrator", the circuit described in the concentrator makes use not only of a line test bus and a terminal test bus each connectable to a multiplicity of test trunks serving each of a group of subscriber lines, but also of a spare bus connectable to the subscriber line test trunks and enabling any of the subscriber lines in a group of lines having a faulty terminal to be connected to any terminal in a group of terminals serving some other group of lines, the terminal in question being connected to no subscriber line and serving as a spare terminal
In the above-mentioned patents, the security circuits also include means for controlling connection means to the spare and to the test apparatuses.
The organization and the means described are naturally specific to copper line technology and cannot be used directly or merely extrapolated for use with optical lines since they are subject to special constraints, particularly with respect to connection and insertion of circuits, which constraints do not exist when using copper lines.
It should also be observed that the above-described circuits are optimized economically for telephone service in which call durations are relatively short and in which there are long periods of low traffic, and they suffer from a structural feature which becomes a major drawback when applied to a multiservice system in which lines have high activity rates and in which the calls on some services last for relatively long periods of time, and this structural feature is the impossibility of performing tests in a group of lines or a line terminal unit that includes a line connected to a spare junctor without simultaneously disconnecting that line from the security means, i.e. without interrupting the service on that line, and this is due to the fact that the connections to the test equipment and the connections to the security means share common items.
Systems are also known for securization of optical links, in particular for long distance transmission, and consist in providing additional optoelectronic components in the interface associated with each line, said components being connected to the lines by switching means using mechanical displacement.
In particular, the present Applicant has described in French patent number FR-A-2 528 586 (=GB-A-2 122 371) "Optical switching devices" a device enabling one laser diode out of four to be selected at the end of an optical fiber, the device comprising a first switching stage comprising two optical changeover switches and a coupling stage constituted by a passive Y-coupler, and in patent application FR-A-2 602 061 (=U.S. Pat. No. 4,759,597), "Mechanical switch for optical fibers", the present Applicant describes a switch suitable for use in the switching stage of the preceding patent.
Such systems cannot be used for providing security for a large number of links for technical and economic reasons: bulkiness of the equipment, and protection limited to failures in the optoelectronic interface components, thus requiring other arrangements to be made to mitigate failures in the electronic circuits in any link.
The object of the invention is to provide a system for connecting optical lines to an exchange,
the system making the following possible:
line and junctor testing by automatic means, and in particular by optical and optoelectronic means included in the lines and the junctors;
testing of lines connected to spare junctors, and the testing of spare junctors regardless of whether they are connected to lines, and without interrupting service on other lines;
the connection of spare junctors only to lines which are observed as being faulty; and
self-testing of the test devices;
the system also not degrading the transmission budgets of optical links regardless of their configuration: nominal; on test; or connected to spare junctors; thereby making it possible to implement spare junctors which are identical to the junctors normally associated with the lines and to implement test circuits using optoelectronic components which are identical to those implemented in the junctors;
the size and the modularity of the system being such as to enable the system to be used in exchanges of various different sizes and whose sizes may change over time; and
system cost should be optimized.